The microstructure and mechanical properties of parent metal for 700L beam steel with different titanium contents and specimens with metal active gas (MAG) welding are compared and studied. The results showed that the ferrite grains in the microstructure of test steel were 3~5 μm, there were a small quantity of deformation bands, yield strength was 678 MPa, tensile strength was 760 MPa and elongation was 17.0% when Ti content was 0.11%; the ferrite grains in the microstructure was 4~8 μm, there were a small quantity of pearlite grains, yield strength was 658 MPa, tensile strength was 734 MPa and elongation was 24.0% when Ti content was 0.07%; the strength of the two types of test steel was increased by about 10 MPa, but elongation was decreased by 1.0 and 3.0 percent points respectively and property of root bending of 180° (d = 2a) was qualified after MAG welding; the content of low carbon martensite was increased and microstructure of heat affected zone for test steel was refined with the increase of Ti content.

Nb-Ti microalloy  /  700L beam steel  /  welding heat affected zone  /  microstructure  /  mechanical properties